We will measure quantitative scattering parameters for biological tissues. These data will be useful to improve utility of diagnostic procedures using reflected or scattered ultrasound in two ways. First, knowledge of the factors which govern the strength of the observed echoes will be useful in the design of clinical apparatus. Second, knowledge of scattering parameters will be useful in differential diagnosis and the identification of particular tissues if the scattered echoes are found to characterize particular tissues. Measurements of amplitude and phase will be made of waves propagated through and scattered from biological tissues. These will be processed to yield absolute scattering parameters such as strength and variance; frequency and angular spectra. These measurements will be tree of the phane cancellation artefact, or the coherent field structure effect we have uncovered. We will determine the mechanisms of scattering by correlating tissue with model measurements and theory, and using fixatives to alter the tissue and identify constituents responsible for scattering. Imaging techniques will be investigated to help identify mechanisms, as well as to evaluate the techniques. The Nahamoo-Kak c.w. procedure will be tested as well as evaluate the techniques. Evaluation will include correlation with the amatomy and pathology of the tissues. Tissues will be selected areas of regular structure first, then slices of organs, whole organs and animals. Comparison of in-vitro and in-vivo results will assure validity. Tissues will include heart and skeletal muscle, liver, and blood vessels in situ, initially. Data exchange with other laboratories is encouraged.